This invention relates to an engine control system, and particularly to that for controlling performance of engines installed in vehicles or vessels, in accordance with various state changes using an inverse model.
Heretofore, a control system using a map has been employed for controlling the air-fuel ratio of an electrically controlled engine, for example. The map is made by collecting data related to a fuel-injection quantity at a certain engine speed and throttle angle, and storing the data in a memory. In actual use, an appropriate air-fuel ratio is determined by detecting an engine speed and a throttle angle, inputting the detected data into the map, determining a fuel-injection quantity based on the map, calculating a compensation most suitable for the operational conditions at the moment or determining the compensation using another map, and inputting the compensation as an actuating value into a drive apparatus system.
However, although an appropriate air-fuel ratio can be obtained by using the control system using a map if operational conditions are normal (i.e., a stable state), it is impossible to conduct appropriate air-fuel ratio control if operational conditions are transient (i.e., a transient state), wherein a throttle angle is changed due to acceleration or deceleration. In the above, after a throttle angle is changed, the change is detected, thereby controlling the air-fuel ratio, and thus, a controlled variable cannot appropriately be determined in accordance with the air or fuel flow. Thus, the control system using a map does not work when the operational state is transient.
In addition, in an engine control system using a feedback system, a controlled variable (control value, e.g., the air-fuel ratio) actually outputted from the engine is fed back to a controlling system, and an actuating parameter (operation value, i.e., fuel injection quantity) of the engine is determined simply based on the actually measured air-fuel ratio and a target air-fuel ratio, thereby constituting a feedback loop having an inverse model-like function.
However, because there is a dead time which is the time for the injected fuel to travel from the fuel injector into a cylinder, a feedback approach using a control value actually outputted from the engine cannot keep up with a change during a transient state of the engine. That is, during a transient state of the engine, a feedback gain cannot be large, resulting in, for example, that an appropriate actuating value cannot be obtained immediately after a throttle valve opens or closes, i.e., it is difficult to track a change during a transient state of the engine (poor transient response). In addition, the engine is easily influenced by environmental changes, and the engine characteristics deteriorate with time. Thus, a discrepancy occurs in the outputted actuating values as a result of environmental changes and eventual engine deterioration. In other words, it is very difficult to accurately model the engine for inverse model control.
Further, there is a great demand in the market for accurate control over the air-fuel ratio even during a transient state, in response to the recent trend of tightening exhaust gas regulations.
An objective of the present invention is to provide an engine control system which is constituted by accurately modeling an engine to allow for tracking changes during a transient state, thereby solving the above problems and satisfying market requirements.